linux-kernel - Re: [PATCH v3 4/4] io_uring: add support for zone-append

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Date:   Wed, 8 Jul 2020 15:22:51 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Kanchan Joshi <joshi.k@...sung.com>
Cc:     Jens Axboe <axboe@...nel.dk>, viro@...iv.linux.org.uk,
        bcrl@...ck.org, hch@...radead.org, Damien.LeMoal@....com,
        asml.silence@...il.com, linux-fsdevel@...r.kernel.org,
        mb@...htnvm.io, linux-kernel@...r.kernel.org, linux-aio@...ck.org,
        io-uring@...r.kernel.org, linux-block@...r.kernel.org,
        Selvakumar S <selvakuma.s1@...sung.com>,
        Nitesh Shetty <nj.shetty@...sung.com>,
        Javier Gonzalez <javier.gonz@...sung.com>
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append

On Wed, Jul 08, 2020 at 06:28:05PM +0530, Kanchan Joshi wrote:
> The last thing is about the flag used to trigger this processing. Will it be
> fine to intoduce new flag (RWF_APPEND2 or RWF_APPEND_OFFSET)
> instead of using RWF_APPEND?
> 
> New flag will do what RWF_APPEND does and will also return the
> written-location (and therefore expects pointer setup in application).

I think it's simpler to understand if it's called RWF_INDIRECT_OFFSET
Then it'd look like:

+	rwf_t rwf = READ_ONCE(sqe->rw_flags);
...
-	iocb->ki_pos = READ_ONCE(sqe->off);
+	if (rwf & RWF_INDIRECT_OFFSET) {
+		loff_t __user *loffp = u64_to_user_ptr(sqe->addr2);
+
+		if (get_user(iocb->ki_pos, loffp)
+			return -EFAULT;
+		iocb->ki_loffp = loffp;
+	} else {
+		iocb->ki_pos = READ_ONCE(sqe->off);
+	}
...
-	ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
+	ret = kiocb_set_rw_flags(kiocb, rwf);